Puffed up magnetsEnergy-harvesting magnets that change their volume when placed in a magnetic field

Puffed up magnetsEnergy-harvesting magnets that change their volume when placed in a magnetic field have been discovered by US researchers. The materials described by Harsh Deep Chopra of Temple University and Manfred Wuttig of the University of Maryland produce negligible waste heat in the process and could displace current technologies and lead to new ones, such as omnidirectional actuators for mechanical devices and microelectromechanical systems (MEMS). [Nature, 2015, 521, 340-343; DOI:10.1038/nature14459]All magnets change their shape but not their volume, even auxetic magnets were previously characterized on the basis of volume conserving Joule magnetostriction. This fundamental principle of volume conservation has remained unchanged for 175 years, since the 1840s, when physicist James Prescott Joule found that iron-based magnetic materials would elongate and constrict anisotropically but not change their volume when placed in a magnetic field, so-called Joule magnetostriction.The work of Chopra, Wuttig changes that observation fundamentally with the demonstration of volume-expanding magnetism. “Our findings fundamentally change the way we think about a certain type of magnetism that has been in place since 1841,” explains Chopra. “We have discovered a new class of magnets, which we call ‘Non-Joulian Magnets,’ that show a large volume change in magnetic fields.” Chopra described the phenomenon to us: “When ‘excited’ by a magnetic field, they swell up like a puffer fish,” he says.Read more. -- source link

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